Radio-frequency bolometer wattmeter



Feb. 5, 1952 E, o. KErzER l-:TAL

RADIO-FREQUENCY BOLOMETER WA'ITMETER 2 SHEETS-SHEET l Filed July 12,1946 "'K :Suveutor 12er, and

Eugene @.Ke Ve rnon .Lndo11 Ottorueg Febfs, 1952 E. o. KEIZER ETALRADIO-FREQUENCY BOLOMETER WTTMETEIR 2 Sl-XEETS--Sl-IEET 2 Filed July 12,1946 ww NN mi NaN @d NN Y l E ugene aKez'zer, and

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D. Landon C82 Gttorneg i Patented Feb. 5, 1952 RADIO-FREQUENCY BOLOMETEBWATTBIETER 'Y Eugene 0. Keizer and Vernon D. Landon, Princeton, N. J.,assignors to Radior Corporation oi America, a corporation of DelawareApplication July 12, 194e, serinNo. 683,055

invention relates to measurement of power at radio vfrequencies andparticularly to Wattmeter systems and components suited for use atultra-high frequencies.

The measurement of power at short wavelengths, for example of the orderof centimeters, has presented unusual difficulties and systemspreviously devised for that purpose have in the main beenunsatisfactory. Many were of complex construction unsuited for eld useand in operation required great care and skill to attain reliablemeasurements under conditions encountered in the field. Others weresuited only for restricted range of measurement, so necessitatingduplication of equipment to cover the required or expected range ofpower to be measured. Still others were inherently inaccurate because ofrandomly variable or uncontrollable factors or need for recalibration byuse of special equipment not available in the field. e

In accordance with the present invention, highfrequency power ismeasurable over a wide range by a wattmeter system which essentiallyneed comprise no more than a section of concentric line, a bolometertube or equivalent, and a direct-current meter responsive to changes inresistance of the bolometer filament. All highfrequency fields andyWattmeter components producing them are within the concentric line andso effectively isolated from influence by or upon external conditions orenvironment. For checklng or recalibration purposes, only a few andcommonly available direct-current components are required.

The invention further resides in features of construction, combinationand arrangement hereinafter described and claimed.

For more detailed understanding of the in-y vention, reference is madeto the accompanying drawings. in which:

Figure 1 shows a wattmeter system with the concentric line unit inperspective and other circuit elements in schematic form; v

Figure 2 is a curve referred to in discussion of the wattmeter of Figure1 8 Claims. (Cl. 171-95) section, of a modification of the elementsshown inFigure 3.-

Referringto Figure l, the cavity I0 generically represents a sourcewhose radio-frequency output is to be determined, for example, anoscillator or radio-frequency power amplifier used in a transmitter ortest equipment. The concentric line II suitably coupled to the source ofpower provides for iow of high-frequency energy therefrom to the loadthefilament of bolometer tube i2. The inner conductor I1 of the line IImay, as shown in Figure 1, extend into the cavity for transfer of energyto the line by capacity coupling, or the transfer may be effected byinductive coupling, for example, by the loop 49 of Figure 6.

The bolometer tube I2 is disposed within the line il with its filament,a ne platinum wire, forming a portion of the inner conductor thereo f.Thus, the energy-dissipation element of the wattmeter and the energypath thereto from power source I0 are within the outer conductor of lineII and isolated thereby from all circuits or circuit components externalto the line.

The bolometer lament,` whose resistance changes as a direct function ofthe radio-frequency power deliveredto the line from the source I0, is incircuit with a variable resistance I3, traversed by direct current froma suitable source, such as a battery. The bolometer filament andmilliammeter I4, in series therewith, are connected in shunt toa portionof the potentiometer resistance I3 selected by adjustment of itscontact. The flow of radio-frequency currents in the resistance I3 andmeter I4, that is, in that portion of the measuring circuit which isexternal vto the Aconcentric line, is prevented as hereinafterspecifically explained. The calibration of the measuring system may beeffected with direct current using, forexample, only a battery, adirect-current voltmeter, a direct-current milli` ammeter and la decaderesistance box. After calibration, and preliminary to a measurement ofhigh-frequency power, the potentiometer resistance I3 is so adjustedthat the meter indi. cates a maximum or predetermined current readingfor zero radio-frequency input toV the line and thereafter upon supplyof radio-frequency power to the line, the meter. readings may betranslated in terms of radio-frequency power of the source I0.

A typical calibration curve using a potentiometer havingI the maximumvalue of 50 ohms; a battery supplying 2 volts, and a milliammeter I4having maximum reading of 30 milliarnperes is shown/in Figure 2. Asapparent from the curve,

this arrangement is highly sensitive vto small amounts of power and yetis useful for reading from the same scale powers ofrelatively largemagnitude; specifically, powers as low as those of the order of 0.01Watt and as high as those of the order of 15 watts may be read withreasonable accuracy;v from lltheisame scales. although .-their ratiois:-1".1-5'00.

In operation, the coupling between the line threaded, as shown in Figure1, to permit the probe I7 or projecting end oftheinnerconductor to bemoved into differentpositions"'Withnythe'v cavity. To adapt thewattmeter for use overa range of frequencies,provisiontisimade'toiadjnst.

its length for tuning of the line as a whoie -:for

Within the main section I5 of line I I the inner conductor 2I isattached to and supported by a pair of spaced blocks 25, of styrol orother suitable insulation, which are secured to the inner surface of theouter conductor 26.

Tofacilitate insertion and removal of the .outer conductor 28 and theshorter inner con- "ductor 29 terminating at the closed end of thealinei-'fformedzfby disc 30 and supported by the 'zwaslier or disc 3| ofstyrol or other suitable insulating material suitably secured to orsnugly engagingtheinner'surface of outer conductor 28.'.lhe..removableisection 21 of line Il is disengageable 'from thebolometer section 320i the the closedfor snorted-endet -the line Iatthef-m'e'an Y frequency of the range of adjustment.

"More specifically, the 'line -II comprisest'he mainjsection I5 whichtelescopicallyreceives'a slidable extensionil 6,*A'adjust'ab'le by theYoperator until maximum Acurrent pto'th'eloa'dris 'indicated' thepower-transfer relations Y"during :continued i.

oper-ation ofsou'rce I Il.- llh'erefore, inV use of' the wattmeten theoperations :are merely "adjustment iniength o'fithe'line 'H Vforvtuningandvariations of coupling to 'eie'ct"maximumreading of the meterI d. Upon Vperformanceof-these "two simple operations jwhich vare not`:affected bychange in position -'of the operator -or any o'fktheextraneous equipment, the powerloutput'mayibe directly read from themeter "I4 or 'from a-'calibration -curve,

such asligur'e '2. The arrangement"as thus-"far describedis"simpleinconstruction and operation,

to formvr spring'. flngerswhich' 'afford' good AV'electrical conta'ct'betweenl *the "outer "conductor *ITB of the slidable *extension`andzthe puter-"cons ductor 'of the main Vsection I5: The'iinnerconductor v2l ofth'emain 'seeti'on'is tubular, atleast' at 'its inputend; tcrreceiveA theinnerconductor section `I Foi the s'lida'lole-extension "I6 'of "the line; to insure 'good "electrical: contactbetween-these twov sections of the *innerponductor 'of 'line Il, the*input endofthe conductor 2I'is*provid"e1 with "s'lots 22; `so to`form'sprin'g iingersvvhich .the 'slidab'le line' extensionv 16."To"s,upp`or.t" and guide the input `end ofinnerconductor section' 2i;there. is provided a second block- 2'4 "offstyr'ol" or other suitableinsulation whi'ch'fis 'suitablysecured within the extension;il6` to .theouterconL ductor I8 thereof and .is providcedY with "a .central opening.of diameterY suitableflidably .toreceive the conductor 2 I.

y..lineflwhosefoutenconductor 33 forms a continuation .of the outerconductor 26 of the main section I5 of the line and-of outer conductor28 of the removable section 21 of the line. The inner conductoroff's'ection 32 lo'fline II formed by the oolom'e'te'riilament "34 Vand:the terminals 35 extending therefrom 'at 'oppositeends otthe bolometertube l2. These'terminalsare received by ithe sockets or axial `openings3'and 31 at `the 'output' andin'put `endsrespectively of theinnerfconductor'sec'tions "2|"and 29 'of the main and "removableYlinesections. I5V "and 21 A'respec tively.V "The outer conductor-33 ofthe'section 32 is provideti with .a slot'38 to aiord clearance for theexhaust.'nipple'X39` of `Athe Lbolometer "tube I2 which'm'ay, forexample, bean'Aerolux H'ZSB. The lengths of the sections `32fand 21 aresuch that.' as 'above mentioned, fthe center. of 'thebolometer'nlarnen't is about ione-half wavelength v.from the 'closedend"30' o'ffthe'line, Vthus tornin'imize variation of fthe current4density 'along the length o"f lthe 'lam'ent To provide for connection.of'lth'e bol'ometer filament in the direct-currentmeasuring circuitincluding resistor I3fandin`e`ter I4, 'and yetfpre ventleakage ofradio-frequency current from the concentric line, there "is utilized'the stub line 40 comprising an' inner conduetorllI whichterminatesinteriolyof line II `at its connection with vtheinnerVconductor 2`Iof .themainsection I5 'of .thelinefandatubularouter-.conductor 42 which :terminates .at.thejunction with theouter .conduetorli of...the-same -section of. thefline. The other-.endof the .stub.1ine .is..close d, .sojfaras .high-.frequencycurrents -areconcerned vby .the disc-.orcap 83.` .The-lengthioi thestubline Ml is anodd number of quarter wavelengthsflong. preferablyione quarterlwavelength dong, so .that theitub.line,zfas :seen fa't-its :input fend`by lthe concentric line, is of 'veryhighrimpedance at out- 'putfrequencies .of source fr0.

For/.itsl-connection to :the-'external measuring circuit, the innerconductor 4I1=exten'ds..through the closed rend P113 ifofilthe .lin'evIandlis insulated therefrom so `.faras -ire'et currentfis concerned, bythe sleeve-44.. the `closed endof the .line IIJ, the 'conductor IYI-isuconne'cted Lto theA cap i543, so far as highefrequencyfounrents'aire1fconcerned, by 'the #by-pass Acondenser '41, `formed by fthe metal1disc`=or plate-t5 v"andfltlfie disc "46 i of mica 'orothersuitableVinsulating ymaterial interposed between fth'e disc A45 'and 'thefend-cap v"43 of- Vvthe line. At 'its input junction'the inner conductor IIIengages the sleeve 43 which surroundsthe inner'conuctor 2i;` of *line-'I I, the sleeve y"ll' coacnng'witnth-e snip v`une Jaci-'afford'stand-pass characteristic. suited for the range offrequeneie's Forlnductively coupling the concentric line H to a source of power, theremay be used the modified construction shown in Figure 6 in which theinner conductor il of Figure 4 is connected to, or formed into, acoupling loop 49. In either case, there is provided a loop 49 whoseterminals are respectively connected to the inner and outer conductorsof the slidable section i6. In this modification, the by-pass condenser4l or equivalent is omitted but a 'oy-pass condenser 53 having this samefunction is provided at the point of feedthrough to the bolometer lamentfrom the external measuring circuit. More specifically, in thismodification the removable end section v2l of Figure 3 is replaced bythe removable end section 21A, Figure 6, having an end disc 30Ainsulated, for direct current, from the inner conductor 29A by theinsulating sleeve 50. The metal disc 5i together with the disc 52 ofldielectric: and the end cap 39A of the line sectionV 27A, form theaforesaid by-pass condenser 53 which precludes or minimizes the ow ofradio-frequency energy from the line il to the external portion of thedirect-current indicating circuit.

Although preferred wattmeter arrangements have been illustrated anddescribed, it shall be understood the invention is not limited theretobut that changes and modifications may be made, all however, within thescope of the appended claims.

We claim as our invention:

1. A high-frequency wattmeter unit comprising a concentric line havingseparable sections whose inner conductor members terminate short of oneanother leaving a gap in the inner conductor of said line, and asingle-electrode bolometer tube removably surrounded by the outerccnductor of one of said sections and having terminals at its oppositeends respectively engaging the ends of said inner conductor members toclose said gaps and to include the bolometer filament in the innerconductor of said line.

2. A high-frequency wattmeter unit comprising a concentric line havingtwo spaced sections, a tubular conductor slidably engaging the outerconductors of said sections to comprise therewith the outer conductor ofsaid line, and a single-electrode bolometer tube removably disposedwithin said outer conductor and whose lament terminals engage the innerconductors of said sections to comprise therewith the inner conductor ofsaid line.

3. A high-frequency wattmeter unit comprising a concentric line havingat one end a telescopic section adjustable to tune the line, having atits other end a section removable for insertion of a bolometer tubewhose filament is to be included in the inner conductor of the line, andhaving intermediate its ends a stub line for connecting or coupling saidline to an external circuit.

4. A high-frequency wattmeter unit comprising a concentric line havingat one end a telescopic section adjustable to tune the line, having atits other end a shorted-end section removable for insertion of abolometer tube whose lament is to be included in the inner conductor ofthe line, and having intermediate its ends a stub line with an insulatedinner conductor connected to said bolometer lament.

5. A high-frequency wattmeter unit comprising a concentric line havingat one end a telescopic section adjustable to tune the line, having atits other end a section removable for insertion of a bolometer tubewhose filament is to be included in the inner conductor of the line, andhaving intermediate its ends a stub line, said stub line and one end ofsaid concentric line being provided with means for connection to anexternal measuring circuit and an external source of high frequency.

6. In a radio-frequency wattmeter of the type including a.direct-current measuring circuit, a coaxial line adapted to receiveradio-frequency power at one end and to be connected to saiddirect-current measuring circuit at a point remote from said end, saidline having an outer hollow conductor extending the length thereof andan inner conductor comprising rod sections extending toward one anotherfrom opposite ends of the line with their adjacent ends spaced from oneanother, and a bolometer tube snugly received within said outerconductor and having a filament extending axially thereof with terminalsrespectively engaged by said spaced ends of the rod sections to completesaid inner conductor for absorption of radio-frequency power and forchanging the resistance of said direct-current circuit as a function ofthe absorbed power,

7. A high-frequency wattmeter unit of the type including adirect-current measuring circuit, comprising a resonant concentric linehaving separable sections whose inner conductor members terminate shortof one another leaving a gap in the inner conductor of the line at anintegral number of half-wavelengths from the closed end of one of saidsections, a bolometer tube insertable in said line and whose filamentcloses said gap for dissipation by the filament of high-frequency energyfed to the open input end of the other of said sections, and a.concentric stub line joining said resonant line between said input endthereof and the bolometer tube to provide to said filament a connectionto said directcurrent measuring circuit which presents high impedance tosaid high-frequency energy.

8. A high-frequency wattmeter as in claim l. in which the electricallength of the concentric line is adjustable over a range of frequenciesand in which an effective portion of the bolometer filament whenincluded in the inner conductor cf said line is about one-halfwavelength from an end of said line at the mean frequency of said rangeso as to obtain maximum dissipation in the bolometer filament.

EUGENE O. KEIZER. VERNON D. LANDON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,106,713 Bowen Feb. 1, 19382,365,207 Moles Dec. 19, 1944 2,399,481 George Apr. 30, 1946 2,411,553Ramo Nov. 26, 1946 2,414,499 Webber Jan. 21, 1947 2,417,820 Ginzton Mar.25, 1947 2,315,671- Tawney Apr. 6, 1947 FOREIGN PATENTS Number CountryDate 545,999 Great Britain June 23, 1942

